Wind turbines are devices that convert mechanical energy to electrical energy. A typical wind turbine includes a nacelle mounted on a tower housing a drive train for transmitting the rotation of a rotor to an electric generator and is other components such as a yaw drive which orientates the wind turbine, several actuators and sensors and a brake. The rotor supports a number of blades extending radially therefrom for capturing the kinetic energy of the wind and causing the driving train rotational motion. The rotor blades have an aerodynamic shape such that when a wind blows across the surface of the blade, a lift force is generated causing the rotation of a shaft which is connected—directly or through a gearing arrangement—to the electrical generator located inside the nacelle. The amount of energy produced by wind turbines is dependent on the rotor blade sweeping surface that receives the action from the wind and consequently increasing the length of the blades leads normally to an increase of the power output of the wind turbine.
Under known control methods the power produced by a wind turbine increases with wind speed until a rated nominal power output is reached and then it is maintained constant. This is done regulating the pitching action of the blades so that the rotor blade's pitch angle is changed to a smaller angle of attack in order to reduce power capture and to a greater angle of attack to increase the power capture. Therefore the generator speed, and consequently, the power output may be maintained relatively constant with increasing wind velocities when this power output corresponds to the nominal power.
The power and rotor speed regulation implemented in most of the known commercial wind turbine control systems is based on controllers, such as a proportional controller (hereinafter referred to as P), a proportional-integral controller (hereinafter referred to as PI), a proportional-derivative controller (hereinafter referred to as PD), and a proportional-integral-derivative controller (hereinafter referred to as PID), that react to already produced errors between controlled variables and its set points with its associated limitations.
In case of gusts and turbulences wind speed may change drastically in a relatively small interval of time requiring relatively rapid changes of the pitch angle of the blades to maintain constant the power output that are difficult to implement taking into account the dynamics of the pitch control actuator, the inertia of the mechanical components and the wind spatial coherence. As a result, it is almost impossible to obtain the theoretically prescribed production in situations with a turbulent wind.
In order to solve this and other problems there are known several proposals of new control systems improving its performance with respect to known controllers such for instance the proposal disclosed in WO 2008/046942 A1.
This invention is addressed to the solution of said problem using known controllers so that it can be implemented in the already installed wind turbines.